Barrett Esophagus: A condition with damage to the lining of the lower ESOPHAGUS resulting from chronic acid reflux (ESOPHAGITIS, REFLUX). Through the process of metaplasia, the squamous cells are replaced by a columnar epithelium with cells resembling those of the INTESTINE or the salmon-pink mucosa of the STOMACH. Barrett's columnar epithelium is a marker for severe reflux and precursor to ADENOCARCINOMA of the esophagus.Esophagus: The muscular membranous segment between the PHARYNX and the STOMACH in the UPPER GASTROINTESTINAL TRACT.Esophageal Neoplasms: Tumors or cancer of the ESOPHAGUS.Metaplasia: A condition in which there is a change of one adult cell type to another similar adult cell type.Precancerous Conditions: Pathological processes that tend eventually to become malignant. (From Dorland, 27th ed)Genes, MCC: Tumor suppressor genes located in the 5q21 region on the long arm of human chromosome 5. The mutation of these genes is associated with the formation of colorectal cancer (MCC stands for mutated in colorectal cancer).Adenocarcinoma: A malignant epithelial tumor with a glandular organization.Cardia: That part of the STOMACH close to the opening from ESOPHAGUS into the stomach (cardiac orifice), the ESOPHAGOGASTRIC JUNCTION. The cardia is so named because of its closeness to the HEART. Cardia is characterized by the lack of acid-forming cells (GASTRIC PARIETAL CELLS).Gastroesophageal Reflux: Retrograde flow of gastric juice (GASTRIC ACID) and/or duodenal contents (BILE ACIDS; PANCREATIC JUICE) into the distal ESOPHAGUS, commonly due to incompetence of the LOWER ESOPHAGEAL SPHINCTER.Endoscopy, Gastrointestinal: Endoscopic examination, therapy or surgery of the gastrointestinal tract.Esophagoscopy: Endoscopic examination, therapy or surgery of the esophagus.Disease Progression: The worsening of a disease over time. This concept is most often used for chronic and incurable diseases where the stage of the disease is an important determinant of therapy and prognosis.Immunohistochemistry: Histochemical localization of immunoreactive substances using labeled antibodies as reagents.Esophagogastric Junction: The area covering the terminal portion of ESOPHAGUS and the beginning of STOMACH at the cardiac orifice.Esophagectomy: Excision of part (partial) or all (total) of the esophagus. (Dorland, 28th ed)Mucous Membrane: An EPITHELIUM with MUCUS-secreting cells, such as GOBLET CELLS. It forms the lining of many body cavities, such as the DIGESTIVE TRACT, the RESPIRATORY TRACT, and the reproductive tract. Mucosa, rich in blood and lymph vessels, comprises an inner epithelium, a middle layer (lamina propria) of loose CONNECTIVE TISSUE, and an outer layer (muscularis mucosae) of SMOOTH MUSCLE CELLS that separates the mucosa from submucosa.Hernia, Hiatal: STOMACH herniation located at or near the diaphragmatic opening for the ESOPHAGUS, the esophageal hiatus.Esophageal Diseases: Pathological processes in the ESOPHAGUS.Pharmacy Administration: The business and managerial aspects of pharmacy in its broadest sense.Esophageal Stenosis: A stricture of the ESOPHAGUS. Most are acquired but can be congenital.Endoscopy: Procedures of applying ENDOSCOPES for disease diagnosis and treatment. Endoscopy involves passing an optical instrument through a small incision in the skin i.e., percutaneous; or through a natural orifice and along natural body pathways such as the digestive tract; and/or through an incision in the wall of a tubular structure or organ, i.e. transluminal, to examine or perform surgery on the interior parts of the body.